Method of metal cladding



Nov. 5, 1968 P. A. DION 3,408,727

METHOD OF METAL CLADDING Filed Jan. 5, 1966 2 Sheets-Sheet l F I6 I A.DION Nov. 5, 1968 FIGZ.

United States Patent '0 f 3,408,727 METHOD OF METAL CLADDING Paul A.Dion, North Attleboro, Mass., assignor to Texas InstrumentsIncorporated, Dallas, Tex., a corporation of Delaware Filed Jan. 5,1966, Ser. No. 518,821 4 Claims. (Cl. 29--474.1)

7 ABSTRACT OF THE DISCLOSURE An aluminum round wire core moves" along apath toward draw rolls in sequence through a drawing and back-tensioningdie, a group of'guide rolls, a peripheral skiving die, and a protectiveatmosphere which is maintained between the skiving die and the rolls.Clean copper strips are electrically resistance-heated and move throughoxide-reducing atmospheres along angular approach paths on oppositesides of the core path and converge on the core within said protectiveatmosphere. The draw rolls form and squeeze the copper strips around thecore with a reduction in the area of the composite cross-section of thecore and strips thereby bonding them in the solid-phase as they aredrawn togther.

This invention relates to metal cladding, and more particularly to thecladding of lengths of metal which are ditiicult to bond metallurgicallyin the solid phase because of oxides difficult to remove.

Among the several objects of the invention may be noted the provision ofmeans for the effective removal of substantially all bond-deterent oxideor other films from the metals to be bonded, including those difficultto remove; the provision of effective means for preventing reformationof oxides before rolling to effect a solidphase metallurgical bond; theprovision of such means which is particularly effective for claddingmetal stripson round or like core-forming wire, rod, tubing or the likeunder the comparatively low reductions imposed by such shapes whenpressurized by rolling and the provision of; space-saving apparatus forcarrying out the improvements. Other objects and features will be inpart apparent and in part pointed out hereinafter.

The invention accordingly comprises the products, constructions andmethods hereinafter described, the scope of the invention beingindicated in the following claims.

In the accompanying drawings, in which one of various possibleembodiments of the invention is illustrated,

, FIG. 1 is a diagrammatic side elevation of apparatus for carrying outthe invention;

FIG. 2 is a diagrammatic cross section taken along line 2-2 of FIG. 1;and

FIG. 3 is a cross section of a finished product.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawmgs.

In US. Patents 2,691,815 and 2,753,623 are disclosed so-called cold andwarm processes for solid-phase bonding. of metal strips undersubstantial physical reductions effected by rolling under pressure. Theprinciples set forth in said patents have also been employed in claddingstrip material on cylindrical core material in the form of wires, rodsand tubes. In this connection see, for example, US. patent applicationSer. No. 63,678, filed Oct. 19, 1960 by Kenneth B. Clark for Forming AndSolid-Phase Bonding, issued as U.S. Patent 3,220,106; and also the US.patent application of said Kenneth B. Clark, Serial No. 93,513, filedMar. 6, 1961 for Manufacture of Clad Rods, Tubing and Clad Tubing,issued as US. Patent 3,220,107. The methods set forth in said patentsand ap- 7 3,408,727 Patented Nov. 5, 1968 2 plications are generallyeffective but in cases of certain core materials some difliculties havebeen encountered which have been costly to avoid. By means of thepresent invention such difiiculties are avoided at low cost.

When it is desired to clad a copper strip or strips on a cylindricalaluminum core by solid-phase roll bonding, it is not feasible, as in thecase of bonding strip to strip, to employ a sufficiently high reductionto break up the stable oxide film that ordinarily forms on aluminum soas to obtain bonding contact between virgin copper and virgin aluminum.Therefore it is desirable to remove the aluminum oxide before bonding.Aluminum oxide is not readily chemically reducible to aluminum in areducing atmosphere. Thus this method. of removal is practicallyforeclosed. If, as may be, the oxide is removed mechanically as byabraiding, skiving, shaving or the like, it reforms rapidly. Forexample, if after such treatment application of pressure for reductionis delayed for even as short a time as a second, the oxide reforms inamounts substantial enough to become a substantial, if not a complete,bond deterrent. Thus it has been found necessary to reduce this time toa half of a second or less, and this has made difiicult the constructionof adequate bonding apparatus.

In the following description the bonding of copper strip to cladaluminum core is used as an example involving the above-mentioneddifficulties, but it is to be understood that the invention isapplicable to other metals that present the same problems. The termmetals as used herein comprehends alloys. The term protective atmospherecomprehends both oxide-reducing and inert atmospheres such as hydrogenand helium.

Referring now more particularly to the drawings, there is shown atnumeral 1 a pair of rolls of a rolling mill designed in the usual way todraw lengths of metal between them and to exert squeezing and sectionreducing pressure. As shown in FIG. 2, the rolls contain peripheralgrooves 3 which are substantially semicircular in cross section andadapted to receive in the bite 2 between them flat strips 5 on oppositesides of an aluminum wire core 7. The dimenisons of the core and stripsare such that the grooves of the rolls transversely bend the stripsaround the core and reduce the total cross section of the assembly underpressure such as will bring about solid-phase bonding between thecopper. and the aluminum, provided they are sufiiciently clean, By thisis meantthat their contacting surface must not only have grosscontaminants removed but also bond-deterrent films such as oxides andthe like.

At numeral 9 is shown a drawing die providing back tension in responseto the drawing action of the rolls 1. This die may also straighten andsize the wire 7. Four idler rolls 11, three of which are shown, guidethe wire core 7 from the die 9 to the nip 2 between rolls 1.

In FIGURE 1 the stipling indicated by the numeral 13 represents theusual highly stable adherent oxide film which rapidly forms over onvirgin aluminum. In order to remove this oxide film 13 there is placedas closely as possible to the rolls 1 an annular inlet skiving orshaving die or other metal removing device 15 designed to skive orotherwise remove the oxide from the core. The structure hereinafterdescribed makes this close placement possible. The die 15 is mountedupon and in the angular recess provided by an angled or forked framework17. The framework 17 forms two gas manifolds 19 having sealing flanges21 engaging marginal portions of the rolls 1 in advance of the bite 2.Packing 4 is employed between the flanges 21 and the rolls 1. Numerals23 indicate gas manifolds each of which has an inlet portion 25 andbackangled portion 27. Each portion 27 connects with one of the gasmanifolds 19. In each manifold 23 is mounted an idling guide roll 29.Each roll 29 receives one of the strips 5 through its inlet portion 25and guides it from manifold 25 to manifold 27 for subsequent passage tothe nip 2 through connected manifold 19. Each set of manifolds 19, 27,23 and 25 is internally connected.

Each manifold portion 27 includes an inlet 31 for the introduction of areducing gas such as hydrogen for flow upwardly through the manifolds27, 23 and 25, then through an outlet provided at 33. Each manifold 19includes a gas inlet 35 into which, if desired, an inert atmosphere suchas helium may be introduced. In the absence of such an inert atmosphere,manifolds 19 may receive reducing atmosphere from a manifold 27. i

At numerals 37 are shown electrical brush contacts for the strips 5.Contacts 37 are in independent'circuits 38 containing controlled powersources 39. The circuits-conmeet with rolls 29. Thus the reaches of thestrip 5 between the brush contacts 37 and the rolls 29 close thecircuit, thus providing for heating of said reaches.

Rolls 29 and 1 could also be connected'to other taps ing or the like toremove gross and other contaminants,-

including oxide. Rotation of the rolls 1 in the direction shown by thedarts draws into the nip 2 the copper strips 5 and the core 7. Thestrips pass in heated condition through air between contacts 37 andmanifolds 25 where reduced oil and other contaminants are oxidized andburned off. The strips 5 then pass through the gas manifolds 25, 23, 27and 19, respectively, wherein the oxides are chemically reduced. Theheating which may for ex-.

ample be at 1600" F. drives off molecular films not theretofore removed.The core 7 may be at room temperature or as much as 300 F. or so. Theheating is also useful for controlling the physical characteristics ofthe strips 5 preparatory to bonding. Some cooling may occur in themanifolds 27 and 19 unless provision is made for additional power inputas described above. The rolls 1 squeeze the copper strips 5 around theskived aluminum wire core 7 as the core is pulled through theback-tensioning drawing die 9 and the circular skiver 15. Thusoxide-free virgin copper and aluminum surfaces are squeezed together byreduction of the composite cross section with a resulting solid-phasebond between all parts 7 and 5. The resulting marginal waste 6 is insome cases squeezed off and falls away, and, if not, it may readily beremoved by suitable bending or skiving. The form of the finished productis shown at 41 in FIGURE 3. It may be subsequently heated to improve thebonds by sintering action.

Aluminum or copper oxide reformation does not occur in manifolds 19because of the existence of reducing or inert gas therein. It will beunderstood that if inert gas is not introduced into the manifold 19, thehydrogen will flow into them from the manifold 27. It will also be seenthat since the skiver 15 is close to the nip 2, the time interval ofcore travel therebetween is short.

The annular skiver 15 removes all aluminum oxide and other contaminants,leaving a virgin aluminum surface against which the cleaned surfaces ofthe strips are brought at the nip space.

A feature of the invention is that the electrical heating of the strips5 may be terminated at substantial distance from the nip 2. Thus thereis provided a dwell time during which the strips may cool somewhat or bemaintained at a constant temperature before entering the nip. Thispermits the strip being taken to temperatures for facilitating copperoxide removal by heating without having the strip unduly hot uponentering the nip. It may be remarked that heretofore when electricalheating was travel between, skiying and bonding. .Thusnf the rolls lused as in US. Patent"3,220,107mentioned above, the connection with thestrip instead of being made at some distance ahead of the nip was madeat the nip by closing the circuit through rolls such as 1. This did notadmit of any dwell time.

It will be noted thatjit i sft utside of each copper strip 5 whichrequires cleaning. and it is other side of the strip that eontatctsitsflrollnthe bonding sure o t p 5 r on he .alitsl gtelpt' id ei.i .q,s..22: and remain clean and uncontaminated all the way through the passline to thenip 2;.

Another advantage of the invention exists by reason of the large anglesA indicated on FIGURE 1. This provides considerable" space close to" thehips: in which the skiving ring ,15 maybe locatedon and between thernanifolds 19, Since, the skiving ring,..1 5 forms an inlet to bothmanifolds 19,. thes kived core, is .not subject to substan-. tialnxidereforrnation beforeit reaches themip More; oyer,.even,.if aprotective atmosphere is-notused in the manifolds 19,,the,fact thatthe.,large, angles Apern rit the skiver lsto ,be brought close to nip 2resultsin ayery short distance. that the virgin. aluminumcore needs to'are,, for example, 7 inches in diameter, a minimum practical distance.is about 3 inches. At a normal product speed of feet a minute, theelapsed time between skiv. ing and bonding is on the order of .30second, that is about A of a second, which is short enough to preventthe substantial reformation of aluminum oxide on the virgin aluminumeven in., air which might leak into the mani-, folds9.

In view of the above, it will be seen that the several objects :of theinvention, are achieved and other advanpanying drawings shall beinterpreted as illustrative and not in a limitingsense.

What is claimedis: I

1. The method of cladding a round metallic core, comprising moving itthrough a round skiving die to peripherallyv cut therefrom oxidizedmetal and expose a virgin metal surface therearound, then moving thecore over a distance to the nip space between grooved draw rolls,maintaining a protective atmosphere around the core material during itsmovement between the skiving die and the nip space rnOving clean stripsof metal cladding material convergently over paths angled with respectto the path of the core and from opposite sides thereof to provide for alocation of the skiving die to minimize the distance between the skiving.die and the nip space, heating said strips, maintaining an oxidereducing atomsphere around the strips as they movealong said paths, saidstrips entering the nip space at points between it and said skiving die,and squeezing the core and cladding material between the rolls with areduction in their composite cross section to effect solid-phasebonding.

2. 'Themethod cladding around aluminum wire core,

comprising moving it through a circular skiving die to peripherally cuttherefrom oxidized metal and expose a virgin aluminum surface entirelytherearound, then tion of said skiving die to provide for said shortdistance heating said strips as they move, and maintainingan oxidereducing atmosphere around said strips unit they reach sadi protectiveatmosphere, said strips entering the nip space at points between it andsaid skiving die, and

squeezing the aluminum core and copper cladding material with areduction in their composite cross section to effect solid-phase bondingbetween the clean surfaces of the strips and the virgin surface of thecore.

3. The method according to claim 1, including the step of passingresistance-heating current through a length of each strip to heat it inits movement through said oxidereducing atmosphere and toward the nipspace.

4. The method according to claim 3, including cooling the strips througha length of each in its movement through said oxide-reducing atmosphereafter heating thereof and before reaching said nip space.

References Cited UNITED STATES PATENTS JOHN F. CAMPBELL, PrimaryExaminer. 10 I. L. CLINE, Assistant Examiner.

PATENT OFFICE UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. 3,408,727 November 5, 1968 Paul A. Dion It is certified thaterrorappears in the above identified patent and that said Letters Patentare hereby corrected as shown below:

Column 1, line 41, "of;" should read of Column 2, line 46, "clean, By"should read clean. By line 57, "forms over on" should read forms on line69, "and back-angled" should read and a back-angled Column 4, lines 8and 9, "surface" should read surfaces line 54, "atomsphere" should readatmosphere line 73, "unit" should read until line 74, "sadi" should readsaid Signed and sealed this 24th day of February 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR.

